1. Field of the Invention
The invention relates to a pulse width modulation amplifier that transforms pulse code modulation (PCM) data into a pulse width modulation (PWM) signal, and amplifies and outputs it, and in particular to a pulse width modulation amplifier that reduces output noise.
2. Description of Related Art
This type of pulse width modulation amplifier has the difficulty of performing a feedback operation for reducing output noise. When the feedback operation is not performed, jitter from a master clock is supplied as output noise as it is. Accordingly, a pulse width modulation amplifier of the prior art has used a technique, by which an output from the pulse width modulation amplifier is provided to a low pass filter to produce an analog signal. The analog signal is transformed to digital data by an analog to digital (A/D) converter, which is feedback to an input. See, for example, Patent Publication Sho 59-183510.
However, the technique has the drawback that since it needs an A/D converter, it has many components and complex circuits and is expensive.
On the other hand, in the prior art, amplifiers, which convert PCM data into an analog signal and then a PWM signal, have been widely used. Because the amplifiers are of analog type, they can easily perform a feedback operation of an output thereof. However, when the processing of PWM is performed based on analog processing, it has the disadvantage that it cannot follow miniaturization of semiconductor process.
As a prior art example coning a pulse width modulation amplifier, there is Utility Model Publication Hei 3-36099.
Accordingly, there is a need for overcoming the disadvantage.